Why would blackouts occur even after the residents heeded the voluntarily cut back of AC use.

I liked both A and B.

A seems to resolve the discrepancy by letting us know that even though the residents cut back on AC use, AC is not the only significant drain. Thus, it is reasonable to see why their lack of use of AC would not necessarily stop the blackouts.

B seems to resolve the paradox because if it is true that most of the air conditioning in the region is used for businesses and factories, then simply cutting back at resident homes may not be enough to stop the blackouts at times.

Same with answer choice (A), the cut back of AC usage at home may not stop the blackouts necessarily because AC is not the only significant drain.

The "discrepancy" in the stimulus is that even if citizens cut back their personal use, the problem will persist unless the heat wave abates. If the issue was being caused by other power sources, the heat wave abating would not stop the blackouts.